Braking systems are used in a large variety of machines and vehicles to control, slow and stop the machine. Exemplary machines include passenger vehicles, trains, dump trucks, and mining vehicles. Moreover, machines increasingly use electric drive systems to provide propulsion. For example, passenger vehicles may use a hybrid drive system whereby a traditional internal combustion engine and an electric motor are used to provide propulsion for the vehicle. Machines, such as a railway engines and off-road vehicles may use a diesel powered engine to drive a generator, which provides electric power to a motor. The motor then provides propulsion for the machine.
Braking systems may take advantage of components in electric drive systems to provide braking for machines. For example, a hybrid passenger vehicle may include a regenerative braking system whereby the vehicle is slowed by the electric drive system while at the same time a battery in the vehicle is recharged and railway engines may use dynamic retarding to slow the train. Although brake systems utilizing electric drive systems have been used, these systems cannot stop a machine traveling at high speed quickly, nor can these systems consistently slow a heavily loaded machine traveling downhill or in slippery conditions.
Some prior systems include a manual retarder lever that enables the operator to control ground speed by manually selecting the level of retarding or automatic retarder control that automatically controls machine speed based upon the operator's machine speed setting. The manual or automatic retarder may control an electric retarding system. Additionally, the operator may control a traditional braking pedal to actuate hydraulic brakes. In this way, the operator can manually control both dynamic retarding and hydraulic brakes. Nevertheless, this configuration may be difficult for an operator to control effectively. For example, if the speed setting lever is set to high, the operator may have to rely more on the service brakes. In a large, heavily loaded machine, this may lead to the service brakes overheating. In addition, excess service brake wear may occur on a machine if the service brakes are used for continuous retarding.
One exemplary braking system is described in U.S. Pat. No. 6,441,573 to Zuber et al. This system describes an electrical and friction braking system. However, the system does not vary the ratio of braking torques based upon user controls, nor based upon whether the electric braking system is meeting the requested retarding needs of the machine.
Some prior systems use brake cooling oil to reduce the risk of the service brakes overheating. Cooling oil may be pumped to the service brakes when they are activated and to minimize the likelihood that the service brakes will overheat. One exemplary brake cooling system is described in U.S. Pat. No. 4,083,469 to Schexnayder and assigned to Caterpillar Inc. The described system includes disc brake assemblies. The assemblies include valves for cooling fluid to communicate with a brake assembly. Cooling flow is automatically activated upon a high temperature condition in the brakes. While the described system will advantageously cool the brakes, it does not direct additional cooling oil flow to brake assemblies based on their actual or expected use in the system.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the disclosure, and thus should not be taken to indicate that any particular element of a prior system is unsuitable for use within the disclosure, nor is it intended to indicate that any element, including solving the motivating problem, is essential in implementing the systems and methods described herein. The implementations and application of the systems and methods described herein are defined by the appended claims.